I think I Meshed this up.

Discussion in 'Software and Applications' started by rithmikansur, Aug 8, 2012.

  1. rithmikansur
    rithmikansur Member
    When i comes to 3D file formats i'm pretty much a total noob.
    I'm curious if someone out there can tell me what the correct terminology is to describe the difference between the two meshes shown in the attached image. At this point i'm not even sure what i should be googling.

    The sphere on the left is an OBJ exported from Sculptris, opened in MeshLab. The sphere on the right is an STL exported from Autodesk Inventor and opened in MeshLab.

    If I attempt to export the sphere on the right as an OBJ and open it in Sculptris, all heck breaks loose. For the sphere i get an error message.
    "too many connections to a vertex". For other shapes, it may import okay.
    BUT, it there's usually a tremendous amount of distortion.

    Any light that can be shed on this is greatly appreciated!
    Thanks in advance!
    Rith.

     

    Attached Files:

  2. stop4stuff
    stop4stuff Well-Known Member
    Basically, Sculptris cannot cope with more than, iirc, 24 lines (face edges) connecting to a vertex (point), although the number may be plus or minus 8.

    The distortion you see from models loaded into Sculptris is due to the way Sculptris works - basically it will try to smooth out any shapes, the fewer faces shapes have, the more the distortion will be. Try loading a cube in and see what happens.

    With your two spheres, the difference is the way the meshes are constructed, the one on the left is more economical with triangle distribution basically for smoother mesh manipulation within Sculptris. As to what the types are called I haven't a clue (sorry) but it may be worth having a dig around on the Scultris website to see if there's any answers there.

     
  3. rithmikansur
    rithmikansur Member
    I see,
    I did check out the Sculptris forum but they didn't seem to know if there was a different name for the different types of meshes.
    I guess maybe there really isn't a difference. It must just be how the software decides to make the mesh. Either that or no one knows..lol

    It's not an elegant solution. But, i was able to lessen the distortion by remeshing/subdividing in MeshLab with the Catmull-Clark or Middle filters. Took some of the guess work away from Sculptris i guess.

    Thanks!
    Rith
     
  4. stannum
    stannum Well-Known Member
    In Blender you get similar spheres to those by using icosphere or uv sphere.
     
  5. rithmikansur
    rithmikansur Member
    Aha! Now that sounds like something i can start googling.
    Thanks!
    Rith
     
  6. tkaap
    tkaap Member
    The left image is closer to a "geodesic" shape, with triangles that are much closer to the same shape as each other.

    The sphere on the right is far easier to write a program to generate, and easier to map UVs onto. (but it has massive polar distortion)

     
  7. You can always take a cube, use subvision(catmull/clark) on it several times. Much less distortion at poles, since there are none.Lol
     
  8. rithmikansur
    rithmikansur Member
    Well I wasn't able to dig up much.
    Other than uv or vsphere and icosphere seem to be the proper terminology to describe them both.
    My end goal was to have inventor choose one type over the other when creating an STL with spherical potions of geometry.
    It appears that its not possible. Not a huge loss. I recapped the offending poles in blender.
    I appreciate everyone's help in seeing the attempt through.
    :)
    Rith
     
  9. designsoul
    designsoul Well-Known Member
    Ah the 'too many connections to a vertex' error
    Subdivision can work.
    A more robust approach for sculptris is to do a VCG surface reconstruction.
    If you set the amount of subvolume splits to 3 or 4 (or higher if your processor can handle it) you will get a mesh with optimized topology. Merge the resulting surfaces and you are ready for import to Sculptris.
     
  10. 8_Perf
    8_Perf Well-Known Member
    Sounds like you got a good handle on this but Ill add what I know. or at least what I think I understand.
    IIRC, when exported as an OBJ, it exports exactly as drawn, if you export as an STL, you force all geometry to be reinterpreted as a collection of triangles, even if it was drawn without them, say if you used "quadface" modeling techniques. Contrary to popular belief, STL did not originally stand for "Stereo Lithography, but rather "Surface Tessellation Language". This language would attempt to interpret any 3d construct as a collection of triangles.
    Im wondering if you took your Sculptres sphere and exported as an STL if it would look more similar to the image on the right. Im guessing yes, but its export engine may not support that many triangles.
     
  11. mkroeker
    mkroeker Well-Known Member
    You two did notice that the thread is six years old ?
     
  12. 8_Perf
    8_Perf Well-Known Member
    Doh!! No I did not. It popped up in my news feed so thought it was current. Maybe for this and other forums, a thread should be automatically locked after say 6 months of no activity.